<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      // 输入：arr=[1, 2, 3, 4]
      // 输出：10
      let arr2 = [1, 2, 3, 4];
      function sum() {
        let sum = arr2.reduce((x, y) => x + y);
        console.log(sum); //求和，10
      }
      sum();
    </script>
  </body>
</html>
